1. Field of the Invention
The present invention relates to a microwave magnetic material body used for a non-reciprocal circuit element used in a microwave band and a method of fabricating the same.
2. Description of the Prior Art
In mobile communication equipment such as a portable telephone or a car telephone, the miniaturization and the diversity thereof have progressed in recent years. Correspondingly, miniaturization and diversity have been also required in a non-reciprocal circuit element used in the above described mobile communication equipment.
Examples of the above described non-reciprocal circuit element include an element having a plurality of center electrodes disposed so as to cross each other in an electrically insulated state and plate-shaped microwave magnetic material bodies disposed on and beneath the plurality of center electrodes and further constructed so that a DC magnetic field is applied to respective portions of the plurality of center electrodes, that is, a so-called lumped-constant type non-reciprocal circuit element. Examples include a lumped-constant type circulator or isolator.
One example of a method of fabricating the above described non-reciprocal microwave circuit element will be described with reference to FIG. 5. A center electrode 42a is disposed on a disc-shaped microwave magnetic material body 41a. The center electrode 42a is in such a shape as to radially extend through the center of the upper surface of the microwave magnetic material body 41a and further lead to the side surface of the microwave magnetic material body 41a. An insulating film 43a made of an insulating material is then disposed on the above described center electrode 42a, and a center electrode 42b is disposed thereon so as to cross the center electrode 42a. Furthermore, an insulating film 43b, a center electrode 42c and an insulating film 43c are disposed in this order on the center electrode 42b, and a microwave magnetic material body 41b is superimposed thereon and fixed. Thereafter, permanent magnets are disposed on and beneath a structure interposed between the above described microwave magnetic material 41a and 41b so that a DC magnetic field is applied to the structure.
The above described microwave magnetic material bodies 41a and 41b have been conventionally fabricated using the following method. Specifically, magnetic powders are put into a metal mold and are press-formed, to obtain a formed body. The formed body obtained is sintered to obtain a microwave magnetic material body 44 shown in FIG. 6. The microwave magnetic material body 44 is mechanically polished so as to have a predetermined thickness, thereby to fabricate a microwave magnetic material body 45 shown in FIG. 7.
As described above, the microwave magnetic material body 45 used for a non-reciprocal circuit element has been conventionally fabricated by obtaining a formed body using a powder press forming process and mechanically polishing a sintered body obtained by sintering the formed body. This process must be used because a thin formed body cannot be fabricated using the powder press forming process. Consequently, a thick formed body must first be fabricated and then a thin microwave magnetic material body 45 is formed by polishing after sintering the thick formed body as described above.
Furthermore, in the conventional method, the powder press forming process has been used to obtain a microwave magnetic material body. Accordingly, metal molds corresponding to the sizes of objective microwave magnetic material bodies are respectively prepared, thereby to cope with the diversity of components. As the miniaturization and the diversity of the components have progressed, however, the various types of metal molds or the like has increased, and the polishing process and the powder forming process have become complicated. As a result, mass productivity is lowered, resulting in very high fabricating costs.